某双螺杆挤出机的螺杆在运行过程中发生早期断裂，通过断口的宏观观察和扫描电镜观察、化学成分分析、显微组织观察、力学性能测试和有限元模拟，找出了螺杆轴断裂失效的原因。结果表明：螺杆轴发生了扭转疲劳断裂，裂纹起源于齿根，且有多个疲劳源；芯轴的花键齿根部是螺杆轴应力集中的部位；热处理工艺欠佳导致材料内部微孔聚集、组织不均匀，这些因素最终致使螺杆轴发生早期疲劳断裂。

A fracture accident of screw shaft of a twin-screw extruder occurred during operation. In order to find the fracture reasons, the failure analysis was carried out by means of macroscopic fracture observation, scanning electron microscope observation, chemical composition analysis,microstructure observation,mechanical property testing and finite element simulation. The results show that torsional fatigue was the cause of the fracture, and the cracks originated from the tooth root, with several fatigue crack sources. Stress concentration at root of the tooth; poor thermal treatment process leads to microporous aggregation and uneven microstructure, these factors were the reasons together caused the screw shaft fracture in the early service life.